Post Common Envelope Binary Stars Prof. Todd Hillwig Summer 2017 1. The Common Envelope Phase

A. When a star on the Red Giant Branch (RGB) or Asymptotic Giant Branch (AGB) “swallows” a nearby companion star B. The envelope is expelled after the two cores spiral together into a tighter orbit C. Produces all close binary stars involving a compact object (white dwarf, neutron star, black hole)

Bulik, T. 2007, Nature 449, 799 2. Central Stars of Planetary Nebulae A. The close binary immediately after the CE phase a) No time for further evolution or changes to the binary b) The surrounding PN is the ejected envelope, so we can study both

Hen Abell 39 M57 -3-401 Ring Nebula 2. Central Stars of Planetary Nebulae B. Studying the properties of these binary stars can tell us i. about the common envelope phase ii. how it effects the stars individually (masses, radii, etc.) iii. the resulting distribution of orbital periods 3. Finding Binary Central Stars A. Brightness Variations a) Generally we find new close binaries through photometric variability – periodic, consistent changes in their brightness b) But it appears many of these systems may have very low amplitudes (< 0.01 mag) – from Kepler spacecraft data

PNG 012.1-11.2 PC 12 3. Finding Binary Central Stars B. Understanding Binarity a) We can work out physical parameters of the system (like masses, radii, and temperatures of the stars) if we also have a radial velocity curve. HaTr 7 3. Finding Binary Central Stars D. Jones et al.: The post-common envelopeA&A central 539, stars A47 o (2012)ftheplanetarynebulaeHenize2-155andHenize2-161

+20 JHK’

Broader+10 Goals • Relationship between0 close binary central stars and− 10other close binaries like CataclysmicRelative declination (arcsec) −20 Variables, Type Ia supernova progenitors,+20 +10 symbiotic0−10 −20 +20 +10 0 −10 −20 +20 +10 0 −10 −20 stars, et? Relative right ascension (arcsec) Fig. 2. Gray-scale representation of the near-IR broad-band J, H,andK′ images of NGC 6778. The gray levels are linear. The coordinate’s origin corresponds to the position of the central star of the nebula detected in the three filters and marked by an arrow in the J image. • What are the relative fractions of Fig. 2. HST images of Hen 2-161 (left,seealso Sahai et al. 2011)andtheNecklace(right; Corradi et al. 2011)highlightingtheirremarkablysimilar PA = 15o +40 o [N II] appearances (elongatedPA = 24 with knotty waists). The image of Hen 2-161 is in the light of Hα+[N II] λ6584 Å, measuring roughly 20′′ 20′′,while different binary types (main sequence × the Necklace image is a colour composite (Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)) measuring roughly 39′′ 35′′. Northern linear jet × Note that theo central star of Hen 2-161 is offset to the northeast from the geometric centre of the nebular ring (in both images, north is up and east PA = 47 companions, whiteis to the dwarf left). companions)Northern knot Cometary knots +20 Table 2. Excerpt of the log of the Hβ-continuum photometric observations and measurements of the central star of Hen 2-155.

Northern curved jet • Mass distribution of central starsJulian date Exposure time Hβ-continuum magnitude Uncertainty on (s) Hβ-continuum magnitude Cometary knots 2455985.7989840 90 15.0020 0.0304 0 o 2455985.8008033 150 15.0008 0.0211 PA = 100 2455985.8029363Equatorial 150 wisps 15.0086 0.0213 2455985.8050782 150 15.0051 0.0211

Relative declination (arcsec) 2455985.8517651 150 14.8521 0.0193

−20 Notes. Full table available in machine-readable format at the CDS. Equatorial wisps

Table 3. Excerpt of theSouthern log ofknot the I-band photometric observations and measurements of the central star of Hen 2-161.

Southern curved jet Southern linear jet Julian date Exposure time I-band magnitude Uncertainty on −40 (s) I-band magnitude 2455987.7904517 45 15.2006 0.0120 +40 +20 0 −20 −40 2455987.7913786 45 15.1932 0.0121 Relative right ascension (arcsec) Fig. 4. NOT composite color picture of NGC 6778 in the [O III](blue), 2455987.7923043 45Hα (green), 15.2113 and [N II](red)emissionlines. 0.0120 Fig. 3. [N II]imageofNGC6778overlaidwiththepositionsoftheslits2455987.8456948 45 15.1422 0.0117 used for the acquisition of the high-dispersion2455987.8466095 echelle spectroscopic 45 ob- 15.1478 0.0116 servations at CTIO (slit width not to scale). Nebular features are also Notes. Full table available in machine-readable format at the CDS. [O III]emissionisenclosedbybright[NII]emission,resulting labeled in the figure. in the highest values of the [N II]/[O III]ratio.This[NII]-bright aperture of the ESO-NTT and the bright nature of the centralstructureon an encompasses absolute scale a using spheroidal catalogue region photometry in the innermost from DENIS sec- star of Hen 2-155, photometric monitoring was possible in Hβtion- (Epchtein of NGC 6778 et al. with 1999 the)andthemethodologydescribedin lowest values in the Hα/[O III]ratioBoffin along acontinuum line close with to the high east-west signal-to-noise direction. ratio Although and with minimal Hα and neb-(theet bluish al. (2012a central), with region an approximate in the composite-color precision of picture). 0.05 mag This (de- [O III]emissionisalsofoundintheseinnermostregions,theular contamination. [O IIIrived]-bright from inner the dispersion region is of tipped detector by zerotwo regionspoints calculated of enhanced from spatial distributionEven with of the the use emission of filters from excluding these the lines majority is much of theHα/each[O III field]ratiosalongthemajoraxisofthebipolarlobes(seen star). The Hβ-continuum observations of Hen 2-155 smoothernebular than emission, that of [N someII].remains, Note also as that such the photometry values of was the ex-in greenishwere also colors placed in onthe an composite-color approximate absolute picture). scale These using chang- stan- [N II]/[OtractedIII]and[N from bothII]/H targetsα ratios with peak an ataperture the location tailored of this to aring. diame-ingdard ratios stars seem observed to imply during that the the observing nebula is runs highly (this ionization- can only be By contrast,ter of roughly the emission 3 the in maximum the Hα and seeing [O III during]linesisbrighter the observationsboundedconsidered along approximate the equatorial due ring, to the while variable the nature bipolar of lobes extinction are along an axis at PA × 20 ,openinginbipolarlobesthatspan density-bounded,during each night although and each some run, shortage however ofas theionizing value photonsof each data at (5′′,thusminimisingthevariablecontaminationintheaperture;∼ ◦ 17′′.AssuggestedinPaperI,theoverallstructureofthecen-Jones 2011). Photometry was performed using the SEXTRAC-theirpoint tips is determined suggested by by the relative enhanced brightness Hα/[O toIII field]ratio. stars no spuri- ∼ tral regionTOR ofsoftware NGC 6778 (Bertin can & be Arnouts described 1996 as), and a bipolar the diff PNerential with mag-a ousThe variability emission can in the have near-IR been introdu imagesced of as NGC part of 6778 this (Fig. process).2) low-ionizationnitude of ring-like the central structure stars measured embedded against within non-variable higher exci- fieldis mostlyAll photometric limited to measurements the innermost and ring-like their uncertainties structure and are to shown the tation bipolarstars. The lobes.I-band observations of Hen 2-161 were then placed[N IIin]-bright Tables 2 regionsand 3 available at the tips at ofthe this CDS. ring. The emission from The composite-color picture in Fig. 4 and the ratio maps in the bipolar lobes of NGC 6778 is hinted at the J image and, to Fig. 5 reveal clear excitation variations within the inner regions alesserextent,attheH image. Given the similaritiesA19, page between 3 of 14 of NGC 6778. At the tips of the equatorial ring, the Hα and the Hα and near-IR images of NGC 6778, we suspect that the

A47, page 4 of 9 4. Student Involvement

A. Ongoing variability survey to discover more binaries a) SARA North b) SARA South c) CTIO 1.3m (queue) d) Kitt Peak 2.1-m (June) e) Kepler spacecraft 4. Student Involvement

B. Observations of new and known but poorly studied systems a) Only about 13 of the 37 catalogued systems are well studied. b) We are collecting photometry of additional systems. c) Spectra from Gemini South & North 4. Student Involvement D. Student Research positions a) Plan ten weeks, starting and ending dates negotiable b) On-campus housing provided (pending approval) c) Data reduction & analysis –photometry & spectroscopy d) Potentially some binary star modeling e) Two positions • Applications through the department • Travel • Kitt Peak (early June) • Maybe: American Astronomical Society Meeting, Maryland (January)